I have a Ford Fiesta as the title reads, the customer complains that the battery keeps going flat, recently within one day trip the car covered 30 miles, then at about teatime the car was stopped at a restaurant and upon trying to start the engine the battery was insufficiently charged to turn the starter motor over fast enough.

No codes are present. The battery has been tested and the printout advises the results are 12.16V, SOC 89% state of charge 45%.

With an amp clamp around the main alternator battery cable at the alternator connection area, charging amps full load is providing initially around 110 amps, which then drops to around 80 amps as the alternator warms up. The charging voltage no load is 13.59V, loaded 12.09V.

I put the scope on the LIN connection and observed a pulsed square wave but the on/off duration of some of the square wave pulses are on for a longer duration than the remaining square waves. I'd upload it but VERUS has its own ShopStream and I have not found a way to copy the file to a USB etc to do anything with it.

Rightly or wrongly, I have had the engine at idle and disconnected the LIN connection no loads on, and the engine initially turned off prior to disconnection, then read the voltage generated from the alternator, which read around 12.42 volts.

With the LIN disconnected and the only feed cable being the main battery feed I'm not sure what excites the alternator, however I am leaning towards the alternator having failed.

Can you be a bit more specific about the vehicle age etc , does it have start stop and a battery monitoring sensor.If the alternator doesnt charge at default rate with the lin isolated and has a good power supply and ground id agree with the generator.However depending on variant ive seen very subtle engine misfires upset the lin bus .Also ensure pin grip is good on lin connector especially if your scope measurment was taken by back probing.Danny

No bms is used in smart regenerative charge systems and is basically used to calculate the battery soc and keep it as near to 85percent as possible .These vehicles can charge at 15.7v quite normal in refresh mode.The lin bus is just a generator co signal sent out from the pcm , the pcm uses its supply voltage as the reference the makes a calculation and applies the cmd signal to increase the charge based on load.Is it is a 1250 sigma engine check for arching around coil towers as this interupts lin signal .You should have a generator lost coms dtc.

Dcunning35 wrote:No bms is used in smart regenerative charge systems and is basically used to calculate the battery soc and keep it as near to 85percent as possible .These vehicles can charge at 15.7v quite normal in refresh mode.The lin bus is just a generator co signal sent out from the pcm , the pcm uses its supply voltage as the reference the makes a calculation and applies the cmd signal to increase the charge based on load.Is it is a 1250 sigma engine check for arching around coil towers as this interupts lin signal .You should have a generator lost coms dtc.

Just quoting it so I can read it at the same time as replying Danny.

When I had VERUS connected I checked for DTC's, there were none stored. When I put the scope on the LIN connection I did have a square wave pulse, but I thought "My opinion" the square wave was irregular. When I loaded the alternator the cmd did not change, at least it appeared that way to me, I would have expected the square wave pulse size to change, but nothing did, the only part of the square wave that looked low to me was the vertical axis at 12v. This engine is the 1.4 SPJC.

Ok so we know its a sigma engine so do check the ht for evidence of arching.The lin is present , granted you say bitewise it doesn't change .So we need to make sure the pcm is seeing a true representation of battery voltage. Use scan tool to check module supply voltage and generator command signal . Meanwhile scope the lin . Load the electrical circuits and look for the supply voltage change, gen cmd alter and subsiquently waveform to change.Have you checked for a battery drain too?Danny

Dcunning35 wrote:Ok so we know its a sigma engine so do check the ht for evidence of arching.The lin is present , granted you say bitewise it doesn't change .So we need to make sure the pcm is seeing a true representation of battery voltage. Use scan tool to check module supply voltage and generator command signal . Meanwhile scope the lin . Load the electrical circuits and look for the supply voltage change, gen cmd alter and subsiquently waveform to change.Have you checked for a battery drain too?Danny

I'll go and check the HT system. Everything else will be later now. I've removed the alternator and am having it bench tested tomorrow, if faulty it will be fixed if not I'll re-install and work my way through your list above.

Just one point I failed to mention twice when replying, sorry my fault, when the engine was running smoothly no misfires etc, I used my Fluke CAT III digital voltmeter to measure voltage from the alternator back to the battery, the same voltage was measured at the B+ terminal of the alternator, along with the same voltage at the battery terminal positive side, I then put the voltmeter leads at each end of the main battery lead to measure volt drop, nothing there so no problem I could see, however on the earth side of the battery to the alternator, I suspected a leaking diode, the reason for this was that when I put the voltmeter probes one at the battery negative terminal and the other probe on the alternator case, I see a voltage of 0.39V, this to me should not be present and I suspect something like a diode in the alternator must be leaking to ground.

I dont see a drop of .39v anything to worry about , you can prove out the drop and its effects with a jumplead from battery earth to engine.As you say your cmd signal doesnt change this means either pcm maxed out signal, pcm lost coms with generator(and we have no supporting dtc) . I would check alternator ripple with clamp, battery voltage and lin to confirm whats not correlating.Again its the pcm supply voltage that gives it the set point.

The battery has been tested and the printout advises the results are 12.16V, SOC 89% state of charge 45%.

Something is, as always, Wrong here !!! So what is the State of Charge(SOC)? Is it 89% or 45% ??? Can't be both !12.16 volts is NOT a good battery - Where the Test Conditions Correct ??

The charging voltage no load is 13.59V, loaded 12.09V.

Not necessarily a fault, lots of prerequisites to meet on Smart Charge, the alternator may not be commanded for Emissions control reasons - Test conditions again ?

I put the

scope on the LIN connection and observed a pulsed square wave but the on/off duration of some of the square wave pulses are on for a longer duration than the remaining square waves

It is Lin Bus, not Duty or Frequency, the human eye will never even begin to analyse it with just a quick glance. Also it carries Bi directional data and not just Command and feedback. Alternator Speed, Temperature, Component ID could easily be riding on it. Would be a project in it self to make sense of it. It is done for you in the PID's

Furthermore, that system has some 40 DTC's specific to Alternator & Charging (all the basis are covered) including DTCs for Alternator Lin Bus. The ECU has no issue with the communication or data. For that reason you can Move On !

Alternator ripple you can check with a Scope AC coupled or even a Power Probe 3 in P to P Mode.

I am leaning towards the alternator having failed.

I think (in the absence of 40+ possible DTC's) the Car needs a New Battery and it is fixed !

A scope on both terminals of the battery and an Amp Clamp around the Negative cable (to eliminate lazy starter) whilst cranking would have spoken volumes in the first 10 minutes and dictated the correct test path from that point on. BASICS !!!

Now that is what you call "Keeping it Simple" !!!

What relevant serial data, actual values, component activations do you have available to you ?

The battery has been tested and the printout advises the results are 12.16V, SOC 89% state of charge 45%.

Something is, as always, Wrong here !!! So what is the State of Charge(SOC)? Is it 89% or 45% ??? Can't be both !12.16 volts is NOT a good battery - Where the Test Conditions Correct ??

The charging voltage no load is 13.59V, loaded 12.09V.

Not necessarily a fault, lots of prerequisites to meet on Smart Charge, the alternator may not be commanded for Emissions control reasons - Test conditions again ?

I put the

scope on the LIN connection and observed a pulsed square wave but the on/off duration of some of the square wave pulses are on for a longer duration than the remaining square waves

It is Lin Bus, not Duty or Frequency, the human eye will never even begin to analyse it with just a quick glance. Also it carries Bi directional data and not just Command and feedback. Alternator Speed, Temperature, Component ID could easily be riding on it. Would be a project in it self to make sense of it. It is done for you in the PID's

Furthermore, that system has some 40 DTC's specific to Alternator & Charging (all the basis are covered) including DTCs for Alternator Lin Bus. The ECU has no issue with the communication or data. For that reason you can Move On !

Alternator ripple you can check with a Scope AC coupled or even a Power Probe 3 in P to P Mode.

I am leaning towards the alternator having failed.

I think (in the absence of 40+ possible DTC's) the Car needs a New Battery and it is fixed !

A scope on both terminals of the battery and an Amp Clamp around the Negative cable (to eliminate lazy starter) whilst cranking would have spoken volumes in the first 10 minutes and dictated the correct test path from that point on. BASICS !!!

Now that is what you call "Keeping it Simple" !!!

What relevant serial data, actual values, component activations do you have available to you ?

Sorry admin error on my behalf, I think others saw through that. The SOH is 89%, the SOC is 45%. The terminal voltage is 12.16v, yes not ideal.

With regard the LIN, comparing the results from the car to examples from here at Pico, the square wave examples are different between their example and my current example, which is why I thought it might be incorrect.

Diode ripple detected at 0.39v, this figure seems high to me I could be wrong. With the alternator LIN plug disconnected and the alternator running the B+ voltage is 12.42v, that is too low and the PCM has been bypassed at that time, in fact I even bypassed ALL car electrics and put my own battery lead on between the alternator and battery, still 12.42v from alternator. My understanding is that if a battery is discharged, not faulty, the alternator will work harder to charge it, this alternator does not seem to be working to me.

One thing about the battery though, it is a 063 lead acid type, should this car have the calcium type battery, this is confusing at the moment as I have read somewhere that not all smart charge systems have a calcium battery fitted.